Elastic tape made from thermoplastic polyurethane (TPU) has many uses, including uses in clothing applications, such as elastic waist bands, bra straps, and the like. Prior art methods to make elastic tape involves extruding a wide sheet of TPU, winding the sheet into a roll, transferring the role to a slitting operation where the wide sheet is slit to the desired narrow width and the narrow tape is wound into individual rolls for later end uses. This prior art method involves multiple steps which adds cost to the elastic tape.
Another prior art method to make the elastic tape is to extrude the TPU into the desired dimensions of the tape. This method also has limitations in the speed at which the tape can be produced. The elastic tape can also be made by dissolving the TPU in solvent and solvent casting the solution into tape. This method has the disadvantage of using solvent.
It is known to produce TPU fibers, either by the dry spinning method or the melt spinning method. The dry spinning method is the most common method commercially used today. The dry spinning method requires solvent and has large initial capital investment requirements. The melt spinning method is more environmentally friendly and requires less capital investment. Both the dry spinning and melt spinning processes are used in making small denier TPU fiber, usually from 10 to 70 denier size. Fiber size is expressed in denier which is the weight in grams of 9000 meters in length of the fiber. Thus, a 20 denier fiber would be one where 9000 meters in length of fibers would weigh 20 grams.
In normal melt spinning or dry spinning of fibers, after the fiber exits the spinneret, it travels through a series of rollers forming a vertical festoon to air cool the fibers before being wound into bobbins. This method works well for small fiber size. When larger denier fibers, such as 100 to 10,000 denier fibers are produced on this type of equipment, the hot fibers will sag or distort when run through the vertical festoon air cooler. The weight of the fibers are too great to be pulled into a vertical position without distorting and the larger size fibers are slower to cool, thus exaggerating the problem.
If a large denier fiber is desired, it is now made by winding several filaments of small denier fiber together to make a large size, such as is done with twine or rope. The multifilament strand can create problems in sewing garments containing the large denier fibers.
It would be desirable to have a melt spinning process for producing elastic tape, heavy denier monofilament fibers as well as other various cross section shapes from TPU.